X-ray CT (Computed Tomography) is a technology with which it is possible to reconstruct an image of the inside of a subject (cross sectional image) based on X-ray intensity distribution (X-ray projection image) obtained by irradiating the subject (physical object) with X-rays from many directions. This type of CT has conventionally been widely used in healthcare applications, and recently has also been used in industry. By using X-ray CT, it is possible to identify a surface shape that cannot be seen from the outside, which makes it useful, for example, in the dimensional inspection and reverse engineering of products having complicated shapes.
In the reconstruction of cross-sectional images in X-ray CT, a regular lattice structure, for example, a mesh formed from a square lattice, is assumed. If a CT value of the outside of a component is made 0 and the CT value of the inside is made 1, in the case where a boundary line that delimits a surface shape (boundary line that separates the component and the outside) passes through a mesh, a CT value of that mesh will be greater than 0 and less than 1, and the surface shape will become blurred. In particular, there are many instances where if shapes of corner sections of a component are blurred, it makes identifying a shape difficult. With healthcare use, it is less problematic to have blurred components, but in industrial use, a solution to the problem of blurred images is necessary in order to identify the surface shape of a product.
On the other hand, the following foreign patent literature describes technology for acquiring images in conformity with the shape of a subject by causing lattice points to move in conformity with a specified shape: Japanese Patent Publication Nos. 2003-123057, 2002-24855, and 2002-74386. However, with each of these technologies, since it is a prerequisite that the shape of a subject has been obtained in advance in some way, it is difficult to apply to a subject of unknown shape. Also, the following foreign patent literature, describes technology for causing the lattice points to move based on a feature plane or feature edge line that has been designated by user: Japanese Patent No. 2007-102595. However, with this technology, even if it is possible to smooth the exterior appearance of an acquired subject shape, it is not always possible to match an acquired subject shape to an unknown subject shape. Also, the technology of Japanese Patent No. 2007-102595 is not for carrying out lattice deformation for matching to an unknown subject shape using values of an acquired cross-sectional image, which means it is not suitable for automatic or mechanical lattice point movement.